1. Field of the Invention
The present invention relates to an apparatus for controlling an idle speed of an internal combustion engine.
2. Description of the Prior Art
In internal combustion engines, at the time of idling when the generated torque is small, the engine speed as a rotating speed of a crank shaft fluctuates with a slight load fluctuation. For example, the engine speed drops at times such as when there is a power load from audio devices, or an air conditioner or the like is turned on, as well as at such times as during steering without driving of a power steering unit or when an automatic transmission is shifted into a Drive range.
On the other hand, in recent years, idle speed has been kept comparatively low due to increased fuel costs, and consequently there is a danger of causing engine stalling in cases where there is overlapping of the main causes which produce load fluctuations, such as those mentioned above.
Because of this, in the typical prior art, the control apparatus which controls an opening degree of the flow control valve provided in an idle bypass pipe takes in the output of the various devices which are the main causes of load fluctuation and the detection results of sensors or the like, and, for example, when the air conditioner is being used, sets a target engine speed when idling of just 250 rpm higher. So as to attain the target engine speed established in this way, together with the adding of a predetermined opening degree for each load to the basic opening degree, an integral control is performed so that the established opening degree will be attained with a small control gain in order to curtail overcontrol.
In prior art such as that mentioned above, since it is necessary for the control apparatus to take in the output from the various devices and the detection results of the sensors or the like, the construction is complicated and the cost rises. Furthermore, since the control gain is low, the responsiveness is inferior and a long time interval is needed to reach the target engine speed. On the other hand, when the control gain is increased, responsiveness improves but stability is inferior. In other words, excesses of control occur leading to overcontrol, and undesirable situations such as so called hunting and quick response are brought about.